The Prime Minister then "stared daggers", which prompted Mr Cable, 70, to give a more powerful jolt and finally rouse the napping Tory, he added.

Mr Balls said he did not know how long Mr Pickles, 61, was slumbering "but given the nature of that speech, it felt like a really, really long time".

At a Westminster briefing he told reporters: "Eric Pickles fell asleep for a quite extended period of time and Ed and I were worried because, you never know, there might have been some big cut in local government spending coming which he didn't know about so we just politely suggested to Vince Cable that he should wake him up.

"Vince elbowed and elbowed but it didn't seem to make any difference. So, Vince was actually knocking away and Eric Pickles... at one point, I think after the third nudge from Vince Cable, Eric started to nod knowingly at the contents of the speech while still with his eyes closed.

"I think eventually David Cameron intervened and he woke up."

"There was a bit of a kerfuffle going on because he was asleep but I think what actually happened is the Prime Minister looked over, stared daggers at Vince and I think Vince may have done a stronger nudge."

Mr Pickles went on Twitter later to protest that he had been wide awake all along – and aides accused the Labour frontbencher of mischief-making.

The Conservative minister said he was "wide awake, although sleep would have been a blessed release from Lab lacklustre response."